Punishment for Hanjuan Jin comes as economic espionage is a growing threat to U.S. companies.

Hanjuan Jin walked on the jet bridge to board a flight to Beijing from O'Hare International Airport. A U.S. Customs officer stopped her as part of a random check of passengers.

A search revealed that Jin was carrying $30,000 in cash in her laptop bag. Her carry-on bags contained Motorola documents marked "confidential and proprietary information."

Jin, a Motorola software engineer, had a one-way ticket.

Five years after Jin was minutes away from flying to China, possibly never to return, she is headed to prison. On Wednesday, she received a four-year sentence for stealing trade secrets from Motorola involving telecommunications technology.

Jin's punishment is among the harshest levied for the crime of trade-secret theft, signaling that law-enforcement authorities and judges are taking criminal cases involving sensitive U.S. technology more seriously. U.S. District Court Judge Ruben Castillo, who presided over Jin's case and convicted her in February after a bench trial, made a point of talking about the value of innovation in handing down Jin's sentence.

"In today's world, the most valuable thing that anyone has is technology," Castillo said. "The most important thing this country can do is protect its trade secrets."

In addition to possessing Motorola files, Jin, 41, also had classified Chinese military documents. While the judge didn't find enough proof to convict Jin on separate charges that her theft intended to benefit the Chinese government, he found the evidence compelling enough to enhance her prison term.

The judge's conclusion elevates Jin's case above an incident of employee wrongdoing into the realm of economic espionage, a growing threat to the U.S. economy, according to a U.S. intelligence report released in November. In the report, the U.S. government accused the Chinese of being the world's "most active and persistent" perpetrators of economic spying.

U.S. companies are prime victims of economic espionage by countries like China and Russia that seek to enhance their domestic industries by acquiring foreign assets and intellectual property. Theft of trade secrets either by insiders or carried out in cyberspace inflicts huge costs on companies, ranging from the loss of intellectual property to the loss of future revenues and profits.

The intelligence report said there are no reliable estimates on the value of such losses. But in specific cases, damages to individual companies have been calculated. For example, an ex-chemist at Valspar Corp. pleaded guilty to stealing proprietary paint formulas worth up to $20 million. In Motorola's case, the company suffered no financial loss resulting from Jin's theft. But the criminal law involving trade secrets allows authorities to calculate intended losses based on research and development costs and other factors. Castillo said the intended loss was $10 million to $15 million.

"We're involved in a war," said Robert Atkinson, president of the Information Technology and Innovation Foundation, a policy think tank in Washington. "It's a war for economic advantage."

With the growing threat to U.S. innovation, the federal government has brought significant resources to combat trade-secret theft. The Motorola and Valspar cases are two of a handful of prosecutions in recent years brought by the U.S. attorney's office in Chicago. A spokesman for the office declined to comment because some cases are pending.

David Glockner, the former chief of the criminal division in the U.S. attorney's office in Chicago, said the prosecutions depend on extensive cooperation of the corporate victims, which have no legal obligation to report a loss of sensitive information or a computer intrusion. Companies also have been reluctant to announce a security breach that could tarnish their reputations. But as cybercrime becomes more pervasive, corporate attitudes are evolving, Glockner said.

"As law enforcement demonstrates that it can handle these type of cases while protecting a company's intellectual property, there has been a greater level of willingness in the private sector to reach out," said Glockner, a managing director at Stroz Friedberg, a digital risk management firm.

The tricky part for law enforcement in trade-secret cases, Glockner said, is figuring out whether the perpetrators are acting out of self-interest or being directed by foreign governments. The penalties are higher in cases where the theft is intended to benefit a foreign government.

Jin's motives are not entirely clear. Castillo said he was dumbfounded by her actions, calling her an "enigma."